1. Technical Field
The invention is related to adjustable stroke controlling mechanisms of the type employed to regulate or set the stroke length of a syringe in order to dispense a prescribed amount of fluid with each stroke of the syringe.
2. Background Art
Mechanisms for regulating or setting the stroke of a syringe to a precise predetermined stroke length corresponding to a desired amount of fluid to be dispensed from the syringe are well-known in the art. U.S. Pat. No. 4,244,366 discloses such a mechanism attached to a syringe and which is adjusted by rotating a threaded metering rod 10 of the mechanism at a knurled adjusting knob 12, as shown in FIG. 1 hereof. Rotation in one direction of the knob 12 lengthens the syringe stroke while rotation in the opposite direction reduces the stroke.
One problem with such a mechanism is that the adjustment from one stroke length to another is tedious and time-consuming, because tile user must rotate the knob 12 many times before the stroke length changes by any appreciable extent, depending upon the pitch of the threads in the metering rod 10. This latter problem is addressed in the above-mentioned U.S. Pat. No. 4,244,366 by providing a threaded nut 14 in fixed position relative to the syringe and engaging the threaded end of the metering rod 10 as shown in FIG. 2 hereof, the nut having a threaded passage 16 and a wider unthreaded passage 18 which opens into the threaded passage 16 through an intermediate opening 20 therebetween of a width sufficient to permit the metering rod 10 to squeeze through with application of some force. Whenever it is desired to quickly make a large adjustment in stroke length, the user forces the metering rod 10 out of the threaded passage 16 through the intermediate opening 20 therebetween and into the unthreaded passage 18. Once in the unthreaded passage, the metering rod 10 slides freely in the longitudinal direction for quick adjustment. Once the metering rod has been moved longitudinally to the desired position, the user forces it back into the threaded portion 16, at which it is held in place by engagement of the threads, permitting some fine adjustment by the user rotating the metering rod 10.
While the foregoing technique of U.S. Pat. No. 4,244,366 permits quicker adjustment of syringe stroke length compared with previous techniques, it has a number of significant problems. Foremost among such problems is that the opening 20 between the threaded and unthreaded passages 16, 18 in the nut 14 must be precisely formed so that it is just large enough so as to not require an undue amount of force to remove or return the metering rod to or from the threaded passage 16, but not so large as to permit the metering rod to inadvertently slip out of the threaded passage 16 at some inopportune moment. Thus, depending upon the precision of manufacture and the wearing of materials over long periods of use, the metering rod 10 might slip through the passage 20.
Another problem with the foregoing is that the required force to dislodge the metering rod from the threaded hole 16 is transverse and as such requires an awkward motion by the user. Moreover, it is a relatively violent motion, increasing the stress and fatigue involved in using such a device.
Accordingly, it is an object of the invention to provide a stroke setting mechanism which is smoothly adjustable using only a small amount of force and requiring no net transverse force across the metering rod and no violent movements or "popping" in or out of a mechanism or rod, so as to minimize fatigue and stress in the user.
It is a further object of the invention to provide a positive guard against slippage of the metering rod from its position set by the user, whereby the mechanism does not require extremely precise tolerances and is not affected by wear of materials over long periods of use.
It is a still further object of the invention to further minimize fatigue by permitting the strength of the entire hand to be employed in plunging the syringe without slippage of finger position on the apparatus.
These and other objects and benefits of the invention will become apparent in the description that follows when taken in conjunction with the drawings.